[PATCH v4 14/59] struct filename: use names_cachep only for getname() and friends

Al Viro
2026-01-08T07:36:50Z

Instances of struct filename come from names_cachep (via
__getname()). That is done by getname_flags() and getname_kernel()
and these two are the main callers of __getname(). However, there are
other callers that simply want to allocate PATH_MAX bytes for uses that
have nothing to do with struct filename.

We want saner allocation rules for long pathnames, so that struct
filename would *always* come from names_cachep, with the out-of-line
pathname getting kmalloc'ed. For that we need to be able to change the
size of objects allocated by getname_flags()/getname_kernel().

That requires the rest of __getname() users to stop using
names_cachep; we could explicitly switch all of those to kmalloc(),
but that would cause quite a bit of noise. So the plan is to switch
getname_...() to new helpers and turn __getname() into a wrapper for
kmalloc(). Remaining __getname() users could be converted to explicit
kmalloc() at leisure, hopefully along with figuring out what size do
they really want - PATH_MAX is an overkill for some of them, used out
of laziness ("we have a convenient helper that does 4K allocations and
that's large enough, let's use it").

As a side benefit, names_cachep is no longer used outside
of fs/namei.c, so we can move it there and be done with that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/dcache.c | 8 +-------
fs/internal.h | 2 ++
fs/namei.c | 37 ++++++++++++++++++++++++++++---------
include/linux/fs.h | 6 ++----
4 files changed, 33 insertions(+), 20 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index dc2fff4811d1..cf865c12cdf9 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3290,10 +3290,6 @@ static void __init dcache_init(void)
runtime_const_init(ptr, dentry_hashtable);
}

-/* SLAB cache for __getname() consumers */
-struct kmem_cache *names_cachep __ro_after_init;
-EXPORT_SYMBOL(names_cachep);
-
void __init vfs_caches_init_early(void)
{
int i;
@@ -3307,9 +3303,7 @@ void __init vfs_caches_init_early(void)

void __init vfs_caches_init(void)
{
- names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0,
- SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL);
-
+ filename_init();
dcache_init();
inode_init();
files_init();
diff --git a/fs/internal.h b/fs/internal.h
index ab638d41ab81..e44146117a42 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -71,6 +71,8 @@ struct dentry *start_dirop(struct dentry *parent, struct qstr *name,
unsigned int lookup_flags);
int lookup_noperm_common(struct qstr *qname, struct dentry *base);

+void __init filename_init(void);
+
/*
* namespace.c
*/
diff --git a/fs/namei.c b/fs/namei.c
index 471e4db2dbdb..468e3db62f53 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -125,6 +125,25 @@

#define EMBEDDED_NAME_MAX (PATH_MAX - offsetof(struct filename, iname))

+/* SLAB cache for struct filename instances */
+static struct kmem_cache *names_cachep __ro_after_init;
+
+void __init filename_init(void)
+{
+ names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0,
+ SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL);
+}
+
+static inline struct filename *alloc_filename(void)
+{
+ return kmem_cache_alloc(names_cachep, GFP_KERNEL);
+}
+
+static inline void free_filename(struct filename *p)
+{
+ kmem_cache_free(names_cachep, p);
+}
+
static inline void initname(struct filename *name)
{
name->aname = NULL;
@@ -164,7 +183,7 @@ getname_flags(const char __user *filename, int flags)
char *kname;
int len;

- result = __getname();
+ result = alloc_filename();
if (unlikely(!result))
return ERR_PTR(-ENOMEM);

@@ -181,13 +200,13 @@ getname_flags(const char __user *filename, int flags)
*/
if (unlikely(len <= 0)) {
if (unlikely(len < 0)) {
- __putname(result);
+ free_filename(result);
return ERR_PTR(len);
}

/* The empty path is special. */
if (!(flags & LOOKUP_EMPTY)) {
- __putname(result);
+ free_filename(result);
return ERR_PTR(-ENOENT);
}
}
@@ -201,7 +220,7 @@ getname_flags(const char __user *filename, int flags)
if (unlikely(len == EMBEDDED_NAME_MAX)) {
struct filename *p = getname_long(result, filename);
if (IS_ERR(p)) {
- __putname(result);
+ free_filename(result);
return p;
}
result = p;
@@ -242,7 +261,7 @@ struct filename *getname_kernel(const char * filename)
struct filename *result;
int len = strlen(filename) + 1;

- result = __getname();
+ result = alloc_filename();
if (unlikely(!result))
return ERR_PTR(-ENOMEM);

@@ -254,13 +273,13 @@ struct filename *getname_kernel(const char * filename)

tmp = kmalloc(size, GFP_KERNEL);
if (unlikely(!tmp)) {
- __putname(result);
+ free_filename(result);
return ERR_PTR(-ENOMEM);
}
tmp->name = (char *)result;
result = tmp;
} else {
- __putname(result);
+ free_filename(result);
return ERR_PTR(-ENAMETOOLONG);
}
memcpy((char *)result->name, filename, len);
@@ -287,10 +306,10 @@ void putname(struct filename *name)
}

if (unlikely(name->name != name->iname)) {
- __putname(name->name);
+ free_filename((struct filename *)name->name);
kfree(name);
} else
- __putname(name);
+ free_filename(name);
}
EXPORT_SYMBOL(putname);

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2244c54d3bfa..e906f157905c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2533,10 +2533,8 @@ static inline int finish_open_simple(struct file *file, int error)
extern void __init vfs_caches_init_early(void);
extern void __init vfs_caches_init(void);

-extern struct kmem_cache *names_cachep;
-
-#define __getname() kmem_cache_alloc(names_cachep, GFP_KERNEL)
-#define __putname(name) kmem_cache_free(names_cachep, (void *)(name))
+#define __getname() kmalloc(PATH_MAX, GFP_KERNEL)
+#define __putname(name) kfree(name)

void emergency_thaw_all(void);
extern int sync_filesystem(struct super_block *);
--
2.47.3